Fix view issue for SQS Reductions in Subject UI

[lcjohnso]

When trying to use the subject view for a workflow that includes an SqsReducer (e.g. https://caesar.zooniverse.org/workflows/7450/subjects/36748525), an error occurs -- see this Sentry issue: https://sentry.io/organizations/zooniverse-27/issues/1563906322/

The source of the problem appears to be the fact that the SqsReducer does not return a key-value pair as expected for reductions, and instead only stores "dispatched" by default as data:

caesar/app/models/reducers/sqs_reducer.rb

Line 23 in b4017d1

r.data = "dispatched" if r.data.blank?